1. Field of the Invention:
This invention relates to photographic cameras and more particularly to a motorized drive device having an electric motor and a transmittion system having at least two speed reduction ratios.
2. Description of the Related Art:
In the past, the winding-up device of the camera had the form of a rapid lever on the upper panel of the camera housing which not only advances the film but also charges the shutter and the lens. Recently, however, the winding-up of the film and the charging have much become motorized. So the manageability has been very improved. In such a progress, there has been a previous proposal for operating the transmission system to the wind-up mechanism with selection of a plurality of speed reduction ratios so that the motor is driven under the optimum condition with the given situations such as the actual voltage of the battery as the power source and the load on the mechanism in U.S. patent applications Ser. Nos. 889,087, 865,063 and 855,799 assigned to the assignee of the invention.
Since this selection of the speed reduction ratios is performed automatically, for the photographer, a problem arises that what speed reduction ratio the camera now sets cannot be seen until the motor is actually driven.
Another problem is that as the speed reduction ratio changes over from the high to the low speed each time the winding-up is recycled, the sound the changeover mechanism makes and the loss of timing becomes a great annoyance to the photographer.
To improve this, the present inventor is considering a measure that after the automatic switching to the low speed has once taken place as the battery voltage fell below the satisfactory operating level for the high speed, the speed reduction ratio of the transmission system is left unchanged from the low speed until the remainder of film in the same cartridge is used up. In this case, however, despite the same film cartridge is in use, if it happens that the ambient temperature situation widely varies from shot to shot (for example, from a skiing ground to the inside of a warm hall), or that the battery recovers, it will become possible to wind up the film or charge the shutter at the high speed. For such an occasion, if the transmission system is unable to set its speed change ratio at the high speed, the versatility of the camera will be halved.
Also, in the above-cited proposal, if the winding and charging mechanisms are provided with respective individual motors and transmission systems, and each of the transmission systems is made to change over between two speed reduction ratios with the use of a speed sensor for detecting the fall of the speed of the windup motor or the charge motor below a critical level, though automatic speed change of all the transmission systems is established, the following problems will have to be solved:
(a) Because the equal number of separate sensors to that of the motors used is necessary, the space and the cost increase.
(b) Because the circuit load of the electrical system becomes large, for a good fidelity is preserved, its cost increases. In particular, recently, the software handling by using a microcomputer prevails. Because the software handling is carried out time-serially, it becomes very difficult to control the operation of the two transmission systems in parallelism.
Meanwhile, another patent application assigned to the assignee of the present invention has proposed a camera having two separate motors for the film winding-up and charging purposes respectively in which when taking continuous shooting, for the purpose of, even though slightly, speeding up the frame rate, if the charging operation of the shutter and lens-diaphragm drive mechanism terminates before the termination of the film winding operation, the next cycle of release operation has, despite the film winding operation in the preceding cycle does not yet terminate, to start in coincidence with the termination of the charging operation of the preceding cycle until just before the shutter is opened.
Such a feature is very advantageous to achieve a great increase in the maximum frame rate so long as the windup transmission system is allowed to run at the high speed. But, if the speed reduction ratio is necessarily set in the low speed, or if the automatic changeover occasionally results in the low speed, the use of the above-described co-ordination control for continuous shooting will bring about a situation that the charging of the various portions of the camera is complete considerably earlier than the winding-up of film is complete. This implies that because the mirror moves upward at the start of the release operation, the photographer, while waiting for the termination of the winding operation, is obliged to look through the light-blocked finder for a long time when the force necessary to pull the film out of the cartridge is high, as this force varies largely depending on the sort of film. Therefore, the higher the force necessary to pull the film out of the cartridge, the longer the time for which the finder gives no view. So, when shooting continuously, the unexpected setting of the windup transmission system in the slow speed will give an awkward impression to the photographer.